The present invention generally relates to gas boosters and, more particularly, to and apparatus and integrated method of modulating a gas booster based upon feedback control of an effective suction flow area of the gas booster.
Gas boosters are used to compress and thereby boost the pressure of the fuel gas that is eventually fed to a turbine engine. Commonly, a metering or control valve is intermediate the gas booster and turbine. The metering valve regulates the amount of fuel into the turbine. Thus, when the turbine is accelerated or decelerated, the metering valve is correspondingly opened or closed.
Previous designs have used a pressure transducer to monitor pressure downstream of the gas booster in order to regulate the metering valve downstream of the gas booster. For example, U.S. Pat. No. 4,087,961 discloses a boost compressor, a pressure regulator downstream of the boost compressor, and a pressure transducer and metering valve downstream of the pressure regulator. A speed governor utilizes the inlet pressure from the pressure regulator and a discharge pressure from the turbine to open or close the metering valve. In turn, the rate of fuel flow into the turbine is controlled.
U.S. Pat. No. 5,305,597 also regulates gas flow at a point downstream of a gas booster and upstream of a turbine. A pressure regulator maintains a constant differential pressure across a metering valve. A mass flow meter is downstream of the metering valve. The metering valve, resolver, and mass flow meter cooperate with an electronic control circuit to generate a feedback signal indicative of the mass fuel flow.
In an effort to reduce the costs associated with using a gas booster, U.S. Pat. No. 4,922,710 attempts to lower the power requirements for the gas booster. A complex series of metering valves downstream of the gas booster minimize pressure drops prior to the turbine.
However, the above past designs do not address fuel control upstream of or at the gas booster. Moreover, the foregoing past designs do not endeavor to provide booster suction control. Yet, gas boosters need an efficient means of compression. The power consumed by the compression process is a function of the fuel delivery rate and the pressure ratio. Therefore, the discharge pressure, or the booster""s ability to deliver fuel at a desired discharge pressure is a primary factor in efficiency. The booster discharge pressure must be high enough to overcome the pressure drops required to meter fuel to satisfy the system needs. Yet, fuel delivered at pressures excessively beyond the system requirements translates into energy wasted.
As can be seen, there is a need for an apparatus and method of regulating the gas delivered to a gas booster. Another need is for an apparatus and method of fuel control upstream of or at the gas booster to provide booster suction control. A further need is for an apparatus and method that improves the efficiency of a gas booster by employing a feedback signal to regulate the delivery of gas to the booster.
In addressing the above needs, the present invention provides in one aspect a method of controlling a gas booster, comprising computing in an engine control unit a reference discharge pressure for the gas booster; comparing in the engine control unit an actual discharge pressure of the gas booster and the reference discharge pressure; generating from the engine control unit a correcting signal derived from the step of comparing; sending from the engine control unit the correcting signal to an inlet valve in flow communication with the gas booster; and adjusting the inlet valve in response to the correcting signal.
In another aspect of the present invention, an apparatus for controlling a gas booster that is used to raise commonly low site pressures of 0.25 to 15 psig to a pressure usable by a turbine engine fuel delivery system comprises a first signal loop having an engine control unit and a receiver of the gas booster, with the said engine control unit being responsive to an actual discharge pressure signal from the receiver; and a second signal loop having the engine control unit and an effective suction flow area of the gas booster, with the effective suction flow area being responsive to a correcting signal from the engine control unit.